This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A177923 #17 Dec 11 2018 12:31:46
%S A177923 19,13,37,23,73,19,23,23,13,59,19,13,13,5,31,7,43,3,53,11,67,131,19,
%T A177923 31,181,11,223,83,317,89,163,569,821,1553,109,191,109,409,709,409,509,
%U A177923 1627,509,23,127,659,809,29,499,191,719,1409,773,967,67,139,23,229,23,11,263,11,19,293,19,331,643,331,29,59,419,13,491,71,23,13,107,13,19,139,19,59,31,109,199,113,421,733,181,89,59,47,13,17,11,41,23,5,23,17,5,5,3,13,7,23,43,73,139,17,229,11,257,71,113,7,191,311,509,337
%N A177923 a(1)=19, a(2)=13, a(3)=37; thereafter a(n) = gpf(a(n-1)+a(n-2)+a(n-3)), where gpf = "greatest prime factor".
%C A177923 This is the periodic part of A177904 - it is periodic with period 212.
%C A177923 A smaller start is a(1)=3, a(2)=13, a(3)=7, but that would not produce the terms in the order of their first appearance in A177904.
%C A177923 There are several open questions concerning this class of sequences - see the Back-Caragiu reference in A177904.
%H A177923 N. J. A. Sloane, <a href="/A177923/b177923.txt">Table of n, a(n) for n = 1..212</a>
%t A177923 nxt[{a_,b_,c_}]:={b,c,FactorInteger[a+b+c][[-1,1]]}; NestList[nxt,{19,13,37},120][[All,1]] (* _Harvey P. Dale_, Dec 11 2018 *)
%Y A177923 Cf. A006530, A177904, A175723.
%K A177923 nonn
%O A177923 1,1
%A A177923 _N. J. A. Sloane_, Dec 18 2010